My father-in-law left some coins, this is one of them. It's pretty black, but it looks like a drachm all the same. I found it hard to capture it, so I made two pictures, one by scanning it and one with my phone. Diameter 17,5 mm, weight 3,97 gr. I wonder what you think of it.
Amazingly difficult to determine whether it is silver or bronze from the photos but the weight and size seem to suggest a very dark silver drachm and the reverse seems typical of those....other than that I'm afraid I have to leave it to those far more familiar with the series. The monogram might indicate Lampsakos???
Antigonos I Monophthalmos, Abydos mint, Price 1560, based on monograms. Compare with the one in this thread: https://www.cointalk.com/threads/help-with-an-alexander-the-great-drachm.270002/
Well, for me it is a substandard coin. But I want to know if it is 'real' - I had some doubt because of the poor style. The one on THC's link has been executed much better.
Although 1.25 months late; I concur with the coin being an AR drachm. I have one also minted under Antigonos I Monophthalmos: You can tell mine was a a cabinet dweller, obverse up, for some time. The obverse has a bronze toning on the protruding areas, with iridescent blue in the valleys; whereas the reverse is left to its natural silver metal.